Mask assemblies used in the treatment of SDB may comprise a nasal mask, designed to fit over a patient's nose, nasal prongs interfacing with a patient's nose, or a full face mask designed to fit over the nose and mouth of the patient. In both cases, the mask may be held in position by headgear.
The mask generally comprises a relatively rigid shell, termed a frame, which defines a rearwardly opening cavity covering the patient's nose and/or mouth and a soft portion, termed a cushion, which contacts and seals against the patient in a preferably comfortable manner.
The air or other breathable gas is supplied by a blower and passed along a flexible conduit to the mask, with the mask frame having a gas inlet that communicates with the conduit.
In addition to the gas inlet, the mask may also have CO2 washout vents and one or more small diameter ports through which supplemental gas such as oxygen may be introduced or through which pressure or other measurements may be made. The ports typically comprise one or more cylindrical connectors molded into the mask frame, usually projecting outwards e.g., forward or downward, from the front surface of the exterior portion of the frame. The mask ports typically also include a cap which may be inserted into or over the ports when the ports are not in use to prevent leakage of air from the mask. Depending on the part construction and the relative diameters of the ports and the tubing which supplies supplemental oxygen, the ports may function as a male or a female connector.
The ports may be provided in alternative locations, such as above, below or on sides of the primary gas inlet and elbow assembly, and there may be one port or more than one port. For example, the Mirage® nasal mask (ResMed Ltd.) is a generally triangular mask with a gas inlet tube connected to an elbow assembly on the front of the mask. The two ports of that mask are located just below the elbow assembly connecting the primary gas inlet and generally adjacent the patient's upper lip region.
When a supplemental gas such as supplemental oxygen is applied through the ports, the gas is delivered to an interior of the mask through the ports, which may not be positioned as close as possible to the patient's nasal region. The location of the ports may thus reduce the effectiveness of delivery of the supplemental gas to the patient as the supplemental gas may escape through the vents or through a leak in the seal between the cushion and the patient's face before the supplemental gas can be delivered to the patient.